The present invention relates to a fuel processor for a fuel cell, and more particularly to a fuel processor for a fuel cell capable of shortening a warm up time.
A polymer electrolyte type of fuel cell includes a stack cell with a polymer electrolyte film sandwiched between an anode and cathode, and generates power through an electrochemical reaction by supplying hydrogen to the anode and oxygen to the cathode.
Since hydrogen ions generated in the anode permeate through the polymer electrolyte film to move to the cathode, in order to hold the ion conductivity of the polymer electrolyte film, it is necessary to supply water to the polymer electrolyte film.
Conventionally, a fuel processor has been used as a source for supplying hydrogen to the fuel cell. The fuel processor vaporizes a raw fuel such as hydrocarbon compound or alcoholic compound and water to create a water/fuel mixed gas and reforms it by using a reforming catalyst, thereby creating a reformed gas containing hydrogen (fuel).
The fuel processor causes the reformed gas to contain excessive water vapor in order to supply water to the polymer electrolyte film of the fuel cell.
Now referring to the drawings, an explanation will be given of the conventional fuel processor for a fuel cell. FIG. 3 shows an entire arrangement of a conventional fuel processor 101.
The fuel processor 101 mainly includes a combustion section 102 for generating a fuel gas, a vaporizing section 103 for vaporizing a mixed solution of raw fuel and water by heat of the combustion gas to create a water/fuel mixed gas, a reforming section 104 for reforming the water/fuel mixed gas by a reforming catalyst to create a reformed gas containing hydrogen, a carbon-monoxide removal section 105 (hereinafter referred to as CO removal section) for oxidizing/removing carbon monoxide by-produced in the reformed gas by a selective oxidizing catalyst and a starting combustion section 106.
The combustion section 102 includes a catalyst for combustion and is provided with a fuel tank 107 for combustion. The vaporizing section 103 is provided with an injecting device 109 equipped with a mixed solution tank 108 via a conduit 110. The mixed solution tank 108 is filled with a mixed solution of raw fuel and water. The raw fuel is usually an alcoholic component such as methanol and a hydrocarbon compound such as methane, ethane and gasoline.
The starting combustion section 106 includes a catalyst for combustion and is provided with a supplying device (not shown) for supplying fuel for starting combustion and air.
The CO removal section 105 is connected to a polymer electrolyte type fuel cell 51 via a conduit 111.
An explanation will be given of the operation until the fuel processor 101 is started to reach a stationary running state.
First, starting fuel is burned in the starting combustion section 106, and the starting combustion gas thus generated is supplied to the reforming section 104 through the conduit 112 to warm the reforming section 104 and CO removal section 105.
At the same time, combustion fuel is burned in the combustion section 102, and the combustion gas thus generated is supplied to the vaporizing section 103 through the conduit 113 to warm the vaporizing section 103.
When the reforming catalyst in the reforming section 104 reaches about 200xc2x0 C. and the vaporizing section 103 reaches the temperature (about 200xc2x0 C.) capable of vaporizing a water/fuel mixed gas, supply of the starting fuel to the starting combustion section 106 is stopped. Simultaneously, the mixed solution is supplied to the injecting device 109 from the mixed solution tank 108 so that the mixed solution is injected into the vaporizing section 103. Then, the mixed solution is vaporized by the heat of the combustion gas supplied from the combustion section 102 thereby to create a water/fuel mixed gas.
The water/fuel mixed gas is supplied to the reforming section 104 via the conduit 114. Simultaneously, the reforming section 104 is supplied with air from the starting combustion section 106. As a result, the raw fuel is reformed into a reformed gas containing hydrogen under the presence of water vapor and oxygen by the reforming catalyst included in the reforming section 104.
The reformed gas is sent to the CO removal section 105 via the conduit 113 so that carbon monoxide by-produced in the reformed gas is oxidized and removed using the selective oxidizing catalyst. The reformed gas thus produced is supplied to the fuel cell 51 via the conduit 111.
In the fuel processor 101 described above, the mol ratio (hereinafter referred to S/C ratio) of steam to carbon(s) (the number of carbon contained in the fuel) in the water/fuel mixed gas is set within a range of 1.5-2.5 so that the mol amount of water vapor in the water/fuel mixed gas is made more than the theoretical reaction mol amount of water in a reforming reaction (in terms of the mol ratio, raw fuel (methanol):water =1:1), thereby leaving the excessive water vapor after the reforming reaction in the reforming gas. Further, by supplying the reformed gas containing the excessive water vapor to the fuel cell 51, water can be supplied to the polymer electrolyte film of the fuel cell 51.
However, the conventional reforming apparatus 101 for a fuel cell has the following problems. In order to increase the S/C ratio of the water/fuel mixed gas is increased, the amount of water to be injected into the vaporizing section 103 is increased. In this case, since the vaporizing heat of water is higher than that of the raw fuel of methanol, a large amount of heat is required to create the water/fuel mixed gas and hence the amount of heat for warming the vaporizing section is reduced. Therefore, it takes a long time to warm the fuel processor 101.
Further, in the conventional reforming apparatus 101, the reforming section 104 and CO removal section 105 are warmed by the starting combustion section 106. In this case, since the CO removal section 105 is provided downstream of the reforming section 104, even when the reforming section 104 is warmed so that the fuel processor 101 reaches its running state, the CO removal section 105 and the conduit 111 downstream thereof are not still warmed (as the case many, the temperature thereof is 80xc2x0 C. or lower).
In this state, when the reformed gas containing water vapor passes the CO removal section 105 and conduit 111, water vapor is condensed into water in the CO removal section 105 and conduit 111. The remaining water reduces the catalytic capability of the selective oxidizing catalyst to lower the removal efficiency of carbon monoxide and closing the flow path of the reforming gas.
It is an object of the present invention to provide a fuel processor for a fuel cell which has a short machine-warming running time and does not provide condensation of water vapor in a reformed gas within the apparatus in a machine-warming running state.
In order to attain the above object, the present invention adopts the following constitution.
The fuel processor for a fuel cell according to the invention includes a vaporizing section for vaporizing water and raw fuel containing hydrocarbon to create a water/fuel mixed gas (vaporizing section 3 in an embodiment); and a reforming section for reforming the water/fuel mixed gas to create a reformed gas containing hydrogen (reforming section 4 in the embodiment).
The fuel processor for a fuel cell further includes adjustable supplying means (first and second injecting devices 12 and 13 in the embodiment) for supplying the raw fuel and the water to the vaporizing section and adjusting a mol ratio of steam to carbon(s) (the number of carbon(s) in the fuel) (hereinafter referred to as xe2x80x9cS/C ratioxe2x80x9d) in the water/fuel mixed gas; temperature detecting means (third thermometer 24 in the embodiment) installed on a deriving flow path (deriving conduit 41 in the embodiment) or device downstream of the reforming section to detect a temperature of the deriving flow path or device; and control means (control means 25 in the embodiment) for controlling the adjusting/supplying means on the basis of the temperature detected by the temperature detecting means.
Now, the device downstream of the reforming section refers to a heat exchanger, carbon monoxide removal section (hereinafter referred to as xe2x80x9cCO removal section), an auxiliary combustion device, and devices provided as necessary, which are located downstream of the reforming section.
The raw fuel may be alcoholic compound such as methanol and hydrocarbon compound such as methane, ethane and gasoline, etc.
In such a fuel processor, on the basis of the temperature detected by the temperature detecting means, the control means determines whether the fuel processor is in a warm up state or a stationary running state. In the machine-warming state, the S/C ratio of the water/fuel mixed gas is controlled to be lower than that in a stationary running state of the fuel processor. In this case, the quantity of water supplied to the vaporizing section is decreased so that the heat quantity required to create the water/fuel mixed gas can be reduced. Thus, the heat quantity used to warm the vaporizing section can be increased, thereby permitting the time for warming the fuel processor to be shortened.
In the warm up state, when the S/C ratio of the water/fuel mixed gas is made lower than that in the stationary running state, even when the water/fuel mixed gas is reformed to create a reformed gas, excessive water vapor is not left in the reformed gas. Therefore, during the warm up running, condensation of water vapor does not occur within the fuel processor, particularly in the deriving flow path or device downstream of the reforming section.
Incidentally, in the warm up state of the fuel processor, the mol ratio of steam to carbon(s) (hereinafter referred to as S/C ratio) in the water/fuel mixed gas is preferably within a range of 0.7-1.2. In the stationary running state, the S/C ratio of the water/fuel mixed gas is preferably within a range of 1.5-2.5.
The adjusting/supplying means comprises a first supplying unit (a first injecting device 12 in the embodiment) for supplying the raw fuel to the vaporizing section and a second supplying unit (second injecting device 13 in the embodiment) for supplying a mixed solution of the raw fuel and water to the vaporizing section.
When the detected temperature is not higher than the stationary running permitting temperature, the control means causes the first supplying unit and second supplying unit to supply the raw fuel and the mixed solution to the vaporizing section, and when the detected temperature has exceeded the stationary running permitting temperature, the control section causes the first supplying unit to stop supply of the raw fuel.
The stationary running permitting temperature refers to a temperature at which water vapor contained in the reformed gas is not condensed in the deriving path or device downstream of the reforming section. Specifically, the temperature is about in the range of 70-80xc2x0 C.
When the detected temperature is not higher than the stationary running permitting temperature, the control means determines that the fuel processor in the warm up running state. On the other hand, when the detected temperature has exceeded the stationary running permitting temperature, the control means determines that the fuel processor is in the stationary running state.
The adjustable supplying means in the fuel processor for a fuel cell, which is under the control by the control means, supplies the raw fuel and mixed solution to the vaporizing section when the fuel processor is in the warm up state, and supplies only the mixed solution to the vaporizing section when the fuel processor in the stationary running state. Thus, the S/C ratio of the water/fuel mixed gas in the warm up running state is made lower than that in the stationary running state, and the S/C ratio of the water/fuel mixed gas in the stationary running state is made higher than that in the warm up running state. In this way, the ratio between the raw fuel and water supplied to the vaporizing section can be easily changed so that the S/C ratio in the water/fuel mixed gas can be easily adjusted.
The fuel reforming device for a fuel cell according to the invention further comprises a combustion section (combustion section 2 in the embodiment) for creating a combustion gas serving as a heat source for the vaporizing section, a bypassing passage (bypass conduit 37 in the embodiment) branching from the way of the deriving passage to supply the reformed gas to the combustion section, and a flow path exchanging valve (three-way cock in the embodiment) arranged at a branching portion of the deriving passage and the bypassing passage.
When the detected is not higher than the stationary running permitting temperature, the reformed gas is supplied to the combustion section via the bypassing passage.
In such a fuel processor, during the warm up running state, the reformed gas is supplied to the combustion section and burned so that the combustion section and vaporizing section can be further warmed.
Further, the reformed gas created during the warm up running contains less quantity of water vapor. Therefore, the heat quantity generated during combustion is increased so that the combustion section and vaporizing section can be further warmed.
The fuel processor for a fuel cell according to the invention vaporizing water and raw fuel to create a water/fuel mixed gas and reforms the water/fuel mixed gas to create a reformed gas are constituted as follows. The temperature of a deriving passage or device supplied with the reformed gas is detected (step S16 in the embodiment). In a machine-warming state where the detected temperature is not higher than a stationary running temperature (step S20 in the embodiment), the S/C ratio of the water/fuel mixed gas is controlled to be lower than that in the stationary running state of the fuel processor (steps S21 and S22 in the embodiment). When the detected temperature has exceeded the stationary running temperature, the S/C ratio of the water/fuel mixed gas is controlled to be higher than that in the machine-warming state (steps S18 and 19 in the embodiment).
In such a fuel processor, in the machine-warming state, the S/C ratio of the water/fuel mixed gas is controlled to be lower than that in a stationary running state of the fuel processor. In this case, the quantity of water supplied to the vaporizing section is decreased so that the heat quantity required to create the water/fuel mixed gas can be reduced. Thus, the heat quantity used to warm the vaporizing section can be increased, thereby permitting the time for warm the fuel processor to be shortened.
In the warm up state, the S/C ratio of the water/fuel mixed gas is controlled to be lower than that in the stationary running state, even when the water/fuel mixed gas is reformed to create a reformed gas, excessive water vapor is not left in the reformed gas. Therefore, during the warm up running, condensation of water vapor does not occur within the fuel processor, particularly in the deriving flow path or device downstream of the reforming section.
The fuel processor for a fuel cell according to the invention is characterized in that when the water/fuel mixed gas is created, in the warm up running state, both the raw fuel and a mixed solution of the raw fuel and water are supplied to the vaporizing section for creating the water/fuel mixed gas (steps S21 and S22 in the embodiment); and in the stationary running state, supply of the raw fuel during the warm up running is stopped and the mixed solution is supplied (steps S18 and S19 in the embodiment).
In such a fuel processor, in the warm up state, the raw fuel and mixed solution to the vaporizing section are supplied to the vaporizing section, and in the stationary running state, only the mixed solution is supplied to the vaporizing section. Thus, the S/C ratio of the water/fuel mixed gas in the warm up running state is made lower than that in the stationary running state, and the S/C ratio of the water/fuel mixed gas in the stationary running state is made higher than that in the warm up running state.
In this way, the ratio between the raw fuel and water supplied to the vaporizing section can be easily changed so that the S/C ratio in the water/fuel mixed gas can be easily adjusted.